Various traditions have different answers on this. There's no consensus. (That may be your answer. The rest may be irrelevant.)
Greg Bala has already addressed the Catholic view. Here are some Protestant ones, ranging from extreme Pentecostal to conservative Christian. None of these are universal. Some groups believe some of them, others think that some of the beliefs are insane, pure guff, or just wrong. I'm not saying which is which, just listing them out.
On the less Charismatic end of the spectrum...
Matthew 7:16 (KJV) Ye shall know them by their fruits. Do men gather grapes of thorns, or figs of thistles?
Galatians 5:16-25 (KJV) 16This I say then, Walk in the Spirit, and ye shall not fulfil the lust of the flesh. 17For the flesh lusteth
against the Spirit, and the Spirit against the flesh: and these are
contrary the one to the other: so that ye cannot do the things that ye
would. 18But if ye be led of the Spirit, ye are not under the law.
19Now the works of the flesh are manifest, which are these; Adultery,
fornication, uncleanness, lasciviousness, 20Idolatry, witchcraft,
hatred, variance, emulations, wrath, strife, seditions, heresies,
21Envyings, murders, drunkenness, revellings, and such like: of the
which I tell you before, as I have also told you in time past, that
they which do such things shall not inherit the kingdom of God. 22But
the fruit of the Spirit is love, joy, peace, longsuffering,
gentleness, goodness, faith, 23Meekness, temperance: against such
there is no law. 24And they that are Christ's have crucified the flesh
with the affections and lusts.
25If we live in the Spirit, let us also walk in the Spirit. 26Let us
not be desirous of vain glory, provoking one another, envying one